Polioencephalomalacia (PEM), also referred to as cerebrocortical necrosis (CCN), is a neurological disease seen in

ruminant Ruminants are herbivorous grazing or browsing artiodactyls belonging to the suborder Ruminantia that are able to acquire nutrients from plant-based food by fermenting it in a specialized stomach prior to digestion, principally through microb ...

s that is caused by multiple factors, one of which is thiamine depletion in the body.

Thiamine Thiamine, also known as thiamin and vitamin B1, is a vitamin – an Nutrient#Micronutrients, essential micronutrient for humans and animals. It is found in food and commercially synthesized to be a dietary supplement or medication. Phosp ...

(vitamin B1) is a key chemical in

glucose metabolism Glucose is a sugar with the molecular formula , which is often abbreviated as Glc. It is overall the most abundant monosaccharide, a subcategory of carbohydrates. It is mainly made by plants and most algae during photosynthesis from water and ...

that, when deficient, is most threatening to neurological activity. In addition to altered thiamine status, an association with high sulfur intake has been observed as a potential cause of PEM. PEM may also be caused by other toxic or metabolic diseases such as: acute

lead poisoning Lead poisoning, also known as plumbism and saturnism, is a type of metal poisoning caused by lead in the body. Symptoms may include abdominal pain, constipation, headaches, irritability, memory problems, infertility, numbness and paresthesia, t ...

salt poisoning Salt poisoning is an intoxication resulting from the excessive intake of sodium (usually as sodium chloride) either in solid form or in solution (saline water, including brine, brackish water, or seawater). Salt poisoning sufficient to produce s ...

. Cattle, sheep, goat, and other ruminants that are diagnosed with PEM or pre-PEM suffer

opisthotonus Opisthotonus or opisthotonos (from and ) is a state of severe hyperextension and spasticity in which an individual's head, neck and spinal column enter into a complete "bridging" or "arching" position. This extreme arched pose is an extrapyram ...

, cortical blindness, disoriented movement, and eventually fatality, if left untreated. Current data shows that the onset of PEM can range from birth to late adulthood.

Causes

Thiamine deficiency

Thiamine availability is controlled by the direct dietary consumption of thiamine. Thiamine availability is also regulated by

thiaminase Thiaminase is an enzyme that metabolizes or breaks down thiamine into pyrimidine and thiazole. It is an antinutrient when consumed. The old name was "aneurinase". There are two types with different Enzyme Commission numbers: * Thiamine pyridi ...

s, which are enzymes that readily cleave thiamine molecules and inhibit essential thiamine-regulated pathways such as the metabolism of glucose. Ruminants have working rumen

microbes A microorganism, or microbe, is an organism of microscopic size, which may exist in its single-celled form or as a colony of cells. The possible existence of unseen microbial life was suspected from antiquity, with an early attestation in ...

that synthesize thiamine molecules for the body; therefore, ruminants do not need to ingest thiamine rich foods for thiamine. However, feed concentrates given to ruminants, specifically sheep and cattle, are often heavily stocked with thiaminases. The presence of thiaminases counter the production of thiamine by breaking them down, resulting in a

futile cycle A futile cycle, also known as a substrate cycle, occurs when two metabolic pathways run simultaneously in opposite directions and have no overall effect other than to dissipate energy in the form of heat. The reason this cycle was called "futile" ...

between rumen microbes and thiaminases. Eventually, when the rate of synthesis production can not exceed thiaminase intake, a state of thiamine deficiency will be reached. Thiaminase rich foods include different grains, fresh water fish, and ferns, all of which are often processed together to make feed concentrate.

Overconsumption of glucose

Since glucose metabolism is regulated by thiamine, the overconsumption of glucose can also result in thiamine inadequacy. When there is a sudden increase of glucose in the body, thiamine will be depleted so that thiamine is not available when the next round of glucose needs to be metabolized.

High sulfur intake

In light of recent research, high concentrations of sulfur intake have also been deemed responsible for PEM.

Sulfur Sulfur ( American spelling and the preferred IUPAC name) or sulphur ( Commonwealth spelling) is a chemical element; it has symbol S and atomic number 16. It is abundant, multivalent and nonmetallic. Under normal conditions, sulfur atoms ...

is necessary for the synthesis of important sulfur-containing amino acids and their contribution to the synthesis of different hormones, enzymes, and structural proteins. The ruminant diet, especially that of cattle, can be overly concentrated with sulfur. In ruminants, the same rumen microbes that generate thiamine molecules reduce sulfur into toxic sulfides. Among the sulfide toxins is

hydrogen sulfide Hydrogen sulfide is a chemical compound with the formula . It is a colorless chalcogen-hydride gas, and is toxic, corrosive, and flammable. Trace amounts in ambient atmosphere have a characteristic foul odor of rotten eggs. Swedish chemist ...

, a gas compound that will compete with oxygen to bind with red blood cells and eventually enter the brain to disrupt neural activity.

Clinical symptoms

Clinical signs of PEM are variable depending on the area of the cerebral cortex affected and may include head pressing, dullness, opisthotonos, central blindness, anorexia, muscle tremors, teeth grinding, trismus, salivation, drooling, convulsions, nystagmus, clonic convulsions, and recumbency. Early administration of thiamine may be curative, but if the lesion is more advanced, then surviving animals may remain partially blind and mentally dull.

References

External links

* at tvsp.org * http://ag.ansc.purdue.edu/sheep/ansc442/Semprojs/2002/neurological/polio.htm * http://www.merckvetmanual.com/mvm/index.jsp?cfile=htm/bc/102000.htm {{Commonscat, Polioencephalomalacia in ruminants Bovine diseases Sheep and goat diseases